The load frames are structural elements within an aircraft fuselage that are characterized by the fact that they support and transfer specific local loads from other structural components such as the vertical tail plane, the horizontal tail plane and the wing. In addition they, of course, comply with the aircraft fuselage shaping and stiffening standard requirements.
Traditionally, load frames were made of metallic materials with different sections, the most common being I and J sections that, through machining processes, are provided with a network of nerves that stabilize the web of the frame.
Despite the tendency to extend the use of composite materials for most of the components of an aircraft due to the weight savings that this material entails with respect to metallic materials, in certain components, such as load frames, it is very difficult, due to their complexity, to achieve a composite material design that can compete both in weight and cost with current metallic designs.
The manufacturing of load frames with composite materials with a similar shape to metallic designs is possible but, apart from the cost resulting from the complexity of their design, it has, among others, the disadvantage that it is very difficult to get optimized laminates for supporting the required loads with these designs, which means not being competitive in weight.
In the case of load frames it is very difficult to compete with the machined metal frames because, due to the high and different loads they shall support, the alternative composite material frames often pose various manufacturing problems due to their rather complex design, with big section changes and areas where all kinds of fabric orientations in the laminate are needed.
Some proposals in this respect are known such as those disclosed in patent applications WO 2008/092970, U.S. 2009/0026315, WO 2009/030731 and EP 2 343 237, but the aeronautic industry continues to demand load frames of composite materials that can compete successfully with metal frames.
The present invention is directed to the attention of that demand.